Telephone and other voice services in IP networks use a plurality of different protocols, referred to as CODECs, which differ in their compromise between compression ratio and quality. For example, in the G.711 codec, voice signals are not compressed at all, while in the G.729 codec, the data signals are compressed in a manner which reduces their quality.
End user devices implementing voice services include telephone sets and media applications, such as voice mail and auto attendant. Different end user devices were designed to use different codecs. At the time of setting up a connection, the opposite end devices participating in the call may exchange lists of codecs which they support to determine a codec which they both support to be used in the connection.
US patent publication 2004/024399, assigned to Nokia corporation and published Dec. 2, 2004, the disclosure of which is incorporated herein by reference, describes a transcoding arrangement in which a session description protocol SDP is used to provide lists of supported codecs.
Similar procedures are described in PCT publication WO02/096040, titled “Communication of Information”, and published Nov. 28, 2002, the disclosure of which is incorporated herein by reference.
In some cases, however, there is no codec that is supported by both the end devices participating in the connection. Therefore, switches (e.g., PBX) that translate signals between different codecs were designed. For example, in order to allow a telephone supporting the G.711 codec to communicate with a telephone supporting the G.729 codec, a switch along the network connecting the telephone translates the signals exchanged between them.
US patent publication 2005/0157708 to Chun, published Jul. 21, 2005, the disclosure of which is incorporated herein by reference, describes a system in which a PBX performs codec translation for a voice mail server.
In addition to providing switches that perform codec translations, manufacturers have provided end user devices that do not support only a single codec, but rather support a large span of codecs. For example, media applications were produced with an additional digital signal processor (DSP) that performs signal translation to a codec used by the main processing unit of the media application. The addition of another DSP for each media application is costly and therefore there have been several suggestions on methods to reduce the cost of the codec translation DSP.
US patent publication 2005/0022255, to Oh, the disclosure of which is incorporated herein by reference, describes a mobile communication terminal which has a main processor and a sub-processor and which distributes codec tasks between them.
U.S. Pat. No. 5,509,009 to Laycock et al., dated Apr. 16, 1996, the disclosure of which is incorporated herein by reference, describes a codec sub-system shared between a plurality of end user devices. Use of such a sub-system reduces the cost of DSPs for the media applications.